One of the most important requirements of a next generation wireless communication system is to support a required high data rate. For this, various techniques such as multiple input multiple output (MIMO), cooperative multiple point transmission (CoMP), relay, etc., have been under research, but the most fundamental and reliable solution is to increase a bandwidth.
However, a frequency resource is in a saturation state at present, and various schemes are partially used in a wide frequency band. For this reason, in order to ensure a broadband bandwidth to satisfy the required higher data rate, a system is designed such that a basic requirement which requires separate bands capable of operating respective independent systems is satisfied. Further, a carrier aggregation (CA) is introduced. In concept, the CA aggregates a plurality of bands into one system. In this case, a band that can be independently managed is defined as a component carrier (CC).
To support growing transmission capacity, the 3GPP LTE or the 802.16m has recently expanded its bandwidth to 20 MHz or higher. In this case, a wideband is supported by aggregating one or more CCs. For example, if one CC corresponds to a bandwidth of 5 MHz, four carriers are aggregated to support a bandwidth of up to 20 MHz. As such, the carrier aggregation system uses a plurality of CCs, and in this sense, it can be called a multi-carrier system.
In order to increase reliability of data transmission in the multi-carrier system, hybrid automatic repeat request (HARQ) can be used. The HARQ is a method in which a receiving end receives data and thereafter reports whether the reception is successful to a transmitting end by using an acknowledgement/not-acknowledgement (ACK/NACK) signal, and the transmitting end transmits new data or retransmits data which fails in reception according to the ACK/NACK signal. Since the multi-carrier system uses a plurality of carriers, data and control information such as resource allocation information can be transmitted in different CCs. In this case, the control information may include a carrier indication field (CIF) indicating a CC on which the data is transmitted. However, there may be a case where the CIF is unnecessary in the process of performing HARQ.